Conventionally, the user utilizes an ordinary or a sophisticated camera to directly take a picture from the screen of a color monitor. There is no electrical connection between the camera and the monitor, and the adjustment of the shutter and aperture of the camera is mechanically controlled. The user encounters the following problems when taking a picture from the screen of the color monitor.
(1) The pixels distributed on the screen are not simultaneously excited by the electronic beams. The picture is formed by the shining of the pixels in sequence. Therefore, it is almost impossible to synchronize the time of the opening of the mechanical shutter with the shining of the pixels of the frame, and it is also almost impossible to match the exposure time of the mechanical shutter with the scanning frame rate of the picture displayed on the screen. As a result, portions of the picture are not subject to the correct degree of exposure; for example, some portions of a picture thus taken by the conventional camera may be brighter and the other portions thereof may be darker than that originally displayed on the screen.
(2) In order to alleviate the above-mentioned drawnbacks, the user may increase the exposure time that the shutter is open for the film and diminish the aperture thereof to alleviate the above-mentioned drawback and get an improved picture. However, it is difficult to get a optimum degree of exposure by the micro-adjustment of the mechanical aperture and/or the mechanical shutter, since a sophisticated instrument is required to calculate the degree of exposure and control the exposure time in order to match with different degree of the brightness of the screens, which is determined depending on the preference of the user. For example, the optimum degree of exposure for the film about a standard brightness of a screen is attained on the condition that the aperture is adjusted at f/22 and the optimum exposure time of the shutter for the film is set at 1/2 second. When taking a picture from the screen of a color monitor, if the period for scanning the screen is 1/60 second per frame, it is obvious that the optimum exposure time should be 30(i.e., 1/2.div.1/60) frames with the standard brightness. If the brightness of the screen is lower than the standard brightness of the screen and the aperture is similarly adjusted at f/22, it may take an exposure of 32 frames to effect the optimum degree of exposure. Therefore, if the user prefers a lower or higher brightness of the screen, he should adjust the shutter or the aperture at the rate of 32: 30 to get an optimum degree of exposure in comparison with the standard brightness. However, it is difficult to adjust to the optimum degree of exposure since the shutter and aperture are mechanically controlled.
(3) In conventional techniques, when taking a picture from the screen of a color monitor, at least one filter is further required to compensate the color deviation not only resulting from the color temperature deviation (i.e., the difference of the spectrum distribution between normal sun light and the light emitted from the screen of a color monitor), but also resulting from the unbalanced weighting of the RGB visual signals on the screen of a color monitor.
It is the purpose of this present invention, therefore, to mitigate and/or obviate the above-mentioned drawbacks in the manner set forth in the detailed description of the preferred embodiment.